Mechanisms of demyelination and remyelination are studied in virus induced demyelinating diseases by means of electron microscopy, immunofluorescence, radioautography and organotypic cultures. The experimental models are murine leukoencephalitis induced by mouse hepatitis virus (MHV) and DA strain of Theiler's encephalomyelitis virus (DAV) and neuritis in chickens caused by Marek's disease virus (MDV). The objectives are to confirm that DAV and MDV induced leukoencephalitis and neuritis are caused by autoimmune mechanisms directed against myelin sheaths. The specific goals are to: 1. Complete comparative morphologic studies on MHV and DAV induced demyelination, 2. Study oligodendroglial replication and remyelination during recovery from these viral infections. 3. Search for lymphocytes with an affinity for myelin basic protein in virus induced demyelinated lesions. 4. Transmit postinfectious autoimmune demyelination by transfer of lymphoid cells. 5. Investigate the development of antimyelin hypersensitivity. 6. Determine the effect of myelin desensitization on the development of postinfectious autoimmunity. 7. Test the sera from infected animals for their ability to demyelinate or to inhibit myelination in organotypic cultures. The findings are expected to contribute to the understanding of the pathogenesis of chronic, postinfectious human demyelinating diseases including multiple sclerosis.